System to store and to transmit electrical power

ABSTRACT

A system to store and to transmit electrical power includes at least one storage system, at least one bidirectional converter, and at least one load coupled to a network, wherein the load is adapted to both, receive electrical power from the network and supply electrical power to the network. A first storage system is used to store electrical power of a power source. The first storage system is connected to a first bidirectional converter by a DC power transmission system. The first bidirectional converter is connected to an AC network and the AC network is connected to a first load.

FIELD OF THE INVENTION

The present invention relates to an energy storage and transmission system, in particular a DC transmission system.

BACKGROUND OF THE INVENTION

Transportation systems are often expected to overcome long distances and to cross areas where suitable power generation systems are not available. Direct current (DC) transmission is a suitable transmission method for economic power transmission over such long distances.

DC transmission systems are known for energy transfer between two remote systems. Thereby, a first converter station is usually located close to the power generation unit at one end of a DC transmission line and a second converter station is located at the other end of the DC transmission line in the load center.

Some more sophisticated DC transmission systems comprise bidirectional converter stations and allow for controlling the current flow direction through the bidirectional converter stations.

Worldwide transportation produces a huge amount of carbon dioxid emissions and thus has a negative impact on the environment. It is therefore desirable to provide transportation systems, especially railway vehicles, with energy from renewable energy sources.

However, transportation systems have to be highly reliable. Renewable energy sources, on the contrairy, are intermittent and their energy output quantity fluctuates.

Besides, the power demand of transportation systems usually fluctuates too because the vehicles start and stop regularly.

It is therefore the object of the present invention to provide an energy storage and transmission system which allows for compensating fluctuations of energy supply and demand.

This object is achieved by means of the independent claim. Advantageous features are defined in the dependent claims. Further objects and advantages are apparent in the following detailed description.

SUMMARY OF THE INVENTION

The present invention discloses a system to store and to transmit electrical power, comprising at least one storage system, at least one bidirectional converter, at least one load coupled to a network, wherein the load is adapted to both, receive electrical power from the network and supply electrical power to the network, wherein a first storage system is used to store electrical power of a power source, wherein the first storage system is connected to a first bidirectional converter by a DC power transmission system, wherein the first bidirectional converter is connected to an AC network and wherein the AC network is connected to a first load.

The system according to the invention incorporates at least one energy storage to compensate energy output variations of at least one energy source. It thus renders possible the use of energy sources with fluctuating energy output for applications requiring an unvarying energy supply.

Thereby, the system according to the invention enables the use of renewable energy sources, e.g. solar or wind power plants, for these applications whithout requiring a national or regional grid acting as energy storage.

Applications requiring an unvarying energy supply comprise transport systems. Thus, the system according to the invention allows for climate-friendly energy supply of transportation systems, for example railway systems.

Advantageously, the system according to the invention allows for bidirectional energy flows. A load not only consumes energy, it may also feed back energy into the system.

It is a further advantage of the present invention that energy feeded in by the load may not only be stored locally, but may also be transferred to the DC transmission system and from the DC transmission system to another storage.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings in which:

FIG. 1: shows a storage and transmission system with a power source connected to the sending end of a DC transmission system through a central storage

FIG. 2: shows a storage and transmission system with power sources connected either directly or through a central storage to the DC transmission system

FIG. 3: shows a storage and transmission system with several power sources and a central storage wherein the power sources and the storage are connected to the DC transmission system

As shown in FIG. 1 the system according to the invention comprises a central storage system CST1. The central storage system is connected to a power source system RES11 and is used to store electrical power which allows for compensating energy output variations of the power source system.

The power source system RES11 comprises either a single power source or several power sources wherein the several power sources are managed in conjunction. Preferably, the power source system comprises renewable power sources like wind or solar power plants.

The aformentioned central storage system CST1 is furthermore connected to bidirectional converter stations CON12, CON13 by a High Voltage Direct Current power transmission system hereinafter called HVDC transmission system. The HVDC transmission system allows for economic power transmission over long distances and for fast control of power flows, not only for the HVDC link but also for surrounding electrical systems.

The central storage system CST1 is connected to the HVDC transmission system through an AC/DC or DC/DC converter station CON11 and comprises a hydrogen storage, a molten salt storage or a pumped hydro storage. Besides, a controller CTR1 is connected to the central storage system CST1.

In addition, a back-up power source BAS1 is connected to the HVDC transmission system through the converter station CON11 for compensating variations of the renewable power source system. The backup power source comprises one or more AC or DC power sources and the converter station CON11 comprises an AC/DC converter or a DC/DC converter, respectively.

The above-mentioned bidirectional converter stations CON12, CON13, are connected to an AC supply network and loads LOA11, LOA12 are coupled to that AC supply network. By way of example these loads are railway vehicles.

The railway vehicles are adapted to both, receive electrical power from the AC supply network and provide electrical power to the AC supply network.

As further shown in FIG. 1, the AC supply network comprises switches SW11, SW21 which allow for segmenting the AC supply network into sub-sections. The sub-sections can be powered independently. Thus only the sub-sections on which a railway vehicle is present could be provided with power.

Thereby, the switches or sub-section interrupters SW11, SW12 are used to couple the first converter station CON12 and the associated first load LOA11 to the second converter station CON13 and the associated second load LOA12 or to decouple the first converter station CON12 and the associated first load LOA11 from the second converter station CON13 and the associated second load LOA12.

The bidirectional converter stations CON12, CON13 comprise DC/AC converters. By means of the bidirectional converter stations, on the one hand, power is feeded into the AC supply network for example to accelerate a railway vehicle or to maintain the vehicles speed, on the other hand, power is harvested from the AC supply network for example during deceleration of a railway vehicle.

Decentral energy storage units DST11, DST12 are either connected to or integrated into these bidirectional converter stations CON12, CON13 to absorb electrical power. Power stored in the decentral storage units DST11, DST12 can be provided to the railway vehicle. The decentral storage units DST11, DST12 may comprise an electrochemical storage (e.g. battery), an electrical storage (e.g. super cap), a mechanical storage (e.g. flywheel energy storage) or any combination thereof.

Energy harvested from the AC supply network may also be fed back to the HVDC transmission system and from the HVDC transmission system to the central storage CST1. Therefore converter CON11 can be a bidirectional converter.

In addition, the storage system CST1, DST11, DST12 and/or the bidirectional converter CON12, CON13 and/or the load LOA11, LOA12 and/or the switch SW11, SW12 and/or the network is connected with an energy management system, which controls energy flows within the system. It further may control the movement of the load LOA11, LOA12 and the switching operation of the switch SW11, SW12.

In an alternate embodiment shown in FIG. 2 further power source systems are connected to the system in addition to the main power source.

As shown in FIG. 2, the system comprises a central storage system CST2 which is connected to a power source system RES21.

That power source system RES21 comprises either a single power source or several power sources wherein the several power sources are managed in conjunction. Preferably, the power source system RES21 comprises renewable power sources like wind or solar power plants.

The aforementioned central storage system CST2 is connected to bidirectional converter stations CON22, CON23 by an HVDC transmission system. Thereby, the central storage system CST2 is connected to the HVDC transmission system directly as well as through an AC/DC or DC/DC converter station CON21. The central storage system CST2 comprises a hydrogen storage and/or a molten salt storage and/or a pumped hydro storage. Besides, a controller CTR2 is connected to the central storage system CST2.

Moreover, a back-up power source BAS2 is connected to the HVDC transmission system through the converter station CON21 for compensating variations of the renewable power source system. The backup power source may comprise one or more AC or DC sources and the converter station CON21 comprises an AC/DC converter or a DC/DC converter, respectively.

The embodiment of the invention shown in FIG. 2, comprises, in addition to the main and backup power sources RES21 and BAS2, further power source systems RES22, RES23 which are connected to the HVDC transmission system. The further power source systems can be located decentrally and may comprise either a single power source or several power sources wherein the several power sources are managed in conjunction. The power source systems RES22 and RES23 may also comprise renewable power sources.

The above-mentioned bidirectional converter stations CON22, CON23 are connected to an AC supply network and loads LOA21, LOA22 are coupled to the AC supply network. By way of example the loads are railway vehicles.

The railway vehicles are adapted to both, receive electrical power from the AC supply network and provide electrical power to the AC supply network.

As further shown in FIG. 2, the AC supply network comprises switches SW21, SW22 which allow for segmenting the AC supply network into sub-sections. The sub-sections can be powered independently. Thus only the sub-sections on which a railway vehicle is present could be provided with power.

Thereby, the switches or sub-section interrupters SW21, SW22 are used to couple the first converter station CON22 and the associated first load LOA21 to the second converter station CON23 and the associated second load LOA22 or to decouple the first converter station CON22 and the associated first load LOA21 from the second converter station CON23 and the associated second load LOA22.

The bidirectional converter stations CON22, CON23 comprise DC/AC converters. By means of these bidirectional converter stations, on the one hand, power is feeded into the AC supply network for example to accelerate a railway vehicle or to maintain the vehicles speed, on the other hand, power is harvested from the AC supply network for example during deceleration of a railway vehicle.

Decentral energy storage units DST21, DST22 are either connected to or integrated into these bidirectional converter stations CON22, CON23 to absorb electrical power. Power stored in the decentral storage units DST21, DST22 can be provided to the railway vehicles. The decentral storage units DST21, DST22 may comprise an electrochemical storage (e.g. battery), an electrical storage (e.g. super cap), a mechanical storage (e.g. flywheel energy storage) or any combination thereof.

Energy harvested from the AC supply network may also be fed back to the HVDC transmission system and from the HVDC transmission system to the central storage system CST2. Therefore the central storage system is directly connected to the HVDC transmission system and converter CON21 is adapted to allow for bidirectional energy flows.

In addition, the storage system CST2, DST21, DST22 and/or the converter CON21, CON22, CON23 and/or the load LOA21, LOA22 and/or the switch SW21, SW22 and/or the network is connected to an energy management system, which controls energy flows within the system. It further may control the movement of the load LOA21, LOA22 and the switching operation of the switch SW21, SW22.

In a further alternate embodiment shown in FIG. 3, the power source systems are located decentrally.

As shown in FIG. 3, a central storage system CST3 is again connected to bidirectional converter stations CON32, CON33 by an HVDC transmission system.

Thereby, the central storage system CST3 is connected to the HVDC transmission system directly as well as through an AC/DC or DC/DC converter CON31. It comprises a hydrogen storage and/or a molten salt storage and/or a pumped hydro storage.

The embodiment shown in FIG. 3, comprises power source systems RES31 and RES32, which are connected to the HVDC transmission system. As aforementioned, these and further power source systems may be located decentrally. They are adapted to provide energy to the central storage system CST3.

The power source systems RES31 and RES32 comprise either a single power source or several power sources wherein the several power sources are managed in conjunction. Preferably, the power sources RES31, RES32 comprise renewable power sources like wind or solar power plants.

In addition, a back-up power source BAS3 is connected to the DC transmission system through the converter station CON31. The backup power source may comprise one or more AC or DC power sources and the converter station CON31 comprises an AC/DC converter or a DC/DC converter, respectively.

The bidirectional converter stations CON32, CON33 are connected to an AC supply network. The loads LOA31 and LOA32 are coupled to that AC supply network. By way of example these loads are railway vehicles.

The railway vehicles are adapted to both, receive electrical power from the AC supply network and provide electrical power to that AC supply network.

As further shown in FIG. 3, the AC supply network comprises switches SW31 and SW31 which allow for segmenting the AC supply network into sub-sections. The sub-sections may be powered independently. Thus only the sub-sections on which a railway vehicle is present could be provided with power.

Thereby, the switches or sub-section interrupters SW31, SW32 are used to couple the first converter station CON32 and the associated first load LOA31 to the second converter station CON33 and the associated second load LOA32 or to decouple the first converter station CON32 and the associated first load LOA31 from the second converter station CON33 and the associated second load LOA32.

The bidirectional converter stations CON32, CON33 comprise DC/AC converters. By means of these bidirectional converter stations, on the one hand, power is feeded into the AC supply network for example to accelerate a railway vehicle or to maintain the vehicles speed, on the other hand, power is harvested from the AC supply network for example during deceleration of a railway vehicle.

Decentral energy storage units DST31, DST32 are either connected to or integrated into these bidirectional converter stations CON32, CON33 to absorb electrical power. Power stored in the decentral storage units can be provided to the railway vehicle. The decentral storage units may comprise an electrochemical storage (e.g. battery), an electrical storage (e.g. super cap), a mechanical storage (e.g. flywheel energy storage) or any combination thereof.

Energy harvested from the AC supply network may also be fed back to the HVDC transmission system and from the HVDC transmission system to the central storage CST3. Therefore the central storage system is directly connected to the HVDC transmission system and converter CON31 is adapted to allow for bidirectional energy flows.

In addition, the storage system CST3, DST31, DST32 and/or the converter CON31, CON32, CON33 and/or the load LOA31, LOA32 and/or the switch SW31, SW32 and/or the network is connected with an energy management system, which controls energy flows within the system. It further may control the movement of the load LOA31, LOA32 and the switching operation of the switch SW31, SW32. 

1-15. (canceled)
 16. A system to store and to transmit electrical power, comprising at least one storage system comprising a central storage system, at least one bidirectional converter comprising a first bidirectional converter, at least one load coupled to an AC network and adapted to both, receive electrical power from the AC network and supply electrical power to the AC network, wherein the at least one load comprises a first load, wherein the central storage system is used to store electrical power of a power source, wherein the central storage system is connected to the first bidirectional converter by a DC power transmission system, wherein the first bidirectional converter is connected to the AC network, and wherein the AC network is connected to the first load.
 17. The system according to claim 16, wherein the at least one bidirectional converter comprises a second bidirectional converter and the at least one load comprises a second load, wherein the central storage system is further connected to the second bidirectional converter by the DC power transmission system, wherein the second bidirectional converter is connected to the AC network, wherein the AC network is connected to the second load, and wherein the AC network comprises a switch being used either to couple the first bidirectional converter and the first load to the second bidirectional converter and the second load or to decouple the first bidirectional converter and the first load from the second bidirectional converter and the second load.
 18. The system according to claim 16, wherein the at least one load is a vehicle.
 19. The system according to claim 16, wherein the central storage system is connected to the DC transmission system directly.
 20. The system according to claim 16, wherein the central storage system is connected to the DC transmission system through an AC/DC converter and/or through a DC/DC converter.
 21. The system according to claim 20, wherein the AC/DC converter) and/or the DC/DC converter is a bidirectional converter.
 22. The system according to claim 16, wherein the central storage system comprises at least one element selected from the group consisting of: a hydrogen storage, a molten salt storage, and a pumped hydro storage.
 23. The system according to claim 16, wherein the at least one storage system further comprises a decentral storage system, and wherein the decentral storage system is connected to the AC network through one of that bidirectional converters.
 24. The system according to claim 23, wherein the decentral storage system is connected to the DC transmission system through one of that bidirectional converters and over that DC transmission system to the central storage system.
 25. The system according to claim 23, wherein the decentral storage system comprises an electro-chemical, an electrical or a mechanical storage.
 26. The system according to claim 16, wherein a controller is connected to the at least one storage system.
 27. The system according to claim 16, wherein an energy management system adapted to control energy flows is connected with at least one element from the group consisting of: the at least one storage system, the at least one converter, the at least one load, a switch, and the AC network.
 28. The system according to claim 27, wherein the energy management system is adapted to control at least one of: the movement of the at least one load, and a switching operation of the switch for selectively powering a sub-section of the network.
 29. The system according to claim 16, wherein the power source comprises at least one power source system which is connected to the DC transmission system.
 30. The system according to claim 29, wherein the power source system comprises renewable power sources selected from the group consisting of: wind power sources, solar power sources and hydro power sources.
 31. The system according to claim 30, wherein the power source system comprises at least one back-up power source is connected to the DC transmission system for compensating variations of the renewable power source. 